Why can't we trust what we see?

The human memory can be impressive, but it is equally prone to letting us down. Now groundbreaking research has revealed the extent of just how fragile it can be - and how to use it better.

You're in the pub and trouble starts. There is shouting, someone is stabbed, they die. It happened right in front of your eyes and the police want to speak to you. But what exactly did you see?

It's long been accepted that eyewitness testimony may not always be as reliable as it seems. The problem is people simply don't remember exactly what happened, say psychologists. The mind does not work like a video camera, nowhere in the brain is the perfect memory of everything that has been seen, in the order it happened.

But however fallible human memory is, it's often the only thing police have to go on and eyewitnesses have been responsible for sending people to prison ever since the justice system began - both rightly and wrongly.

Now research has gone further than ever before to understand the fragile nature of our powers of recall.

The project - involving the Open University, the BBC and Greater Manchester Police (GMP) - is groundbreaking in several ways. The technology it used is cutting edge, including eye trackers - devices for measuring eye positions and eye movement. But just as unparalleled was the realism involved. It's always a big issue with research - how do you accurately test someone's everyday reactions when they know they are part of an experiment and in controlled conditions? Won't they try harder to remember details if they know they are doing a memory test?

'Appalling'

In this case the important action took place when they were least expecting it. The 10 volunteers were put through days of memory tests in a studio and assumed this was the research. In fact, two intricately planned and elaborate mock crimes - a fatal stabbing and an armed robbery - were really what mattered.

On one day the participants went for lunch in a local pub, which was really filled with actors, stuntmen and 10 hidden cameras. A fight broke out and someone appeared to be stabbed and killed. The whole scenario unfolded over 20 minutes.

EYEWITNESS SIMON WOODTHORPE

The whole experience really surprised me. I'd never had a problem with my memory before but had never been in a situation where I'd been asked to recall things in that much detail.

I was good at describing the overall situation. But when it came to the real detail of what had happened, I was actually creating a lot of what I thought I'd remembered.

I'm not sure I would be confident about saying I'd seen anything after this. I'd be worried about incriminating someone.

"It was incredibly realistic," says Simon Woodthorpe, 44, a photographers' agent who was one of the volunteers. "We weren't expecting it at all and only started to get suspicious when the police turned up really quickly. By then it didn't matter, we'd not suspected it was staged so we hadn't consciously thought about paying extra attention to all the details.

"I always thought I had a good memory, but I was yards away from the incident, saw it all unfold and still got the murderer wrong. I said it was the wrong man."

What was also unprecedented about the project was the access to interviewing techniques used by GMP. Detectives treated each mock crime as if it were real, interviewing the volunteers, but unlike a real case, the force's conclusions about what had happened could be checked against what exactly went on. It was a real test of their skill.

During the drama the eye trackers - still being worn by some volunteers during the mock robbery - were able to pinpoint exactly what people were looking at and compared to what they reported. The differences, say those involved, were in some cases staggering.

'Lifeblood'

"One person thought they hadn't seen the crime being committed, they were adamant about it," says Dr Graham Pike, a memory expert involved in the project. "When we reviewed the eye tracker we found they'd actually spent almost the entire time looking at it unfold. It was quite amazing."

FIND OUT MORE

Episode one of the three-part Eyewitness is broadcast on BBC Two beginning on Sunday 18 April at 2250 BST

What makes the memory this vulnerable is the fact it is malleable and not fixed, says Dr Pike.

"It's not like inputting data into a computer, the mind does not store facts absolutely the way they are and it does not recall them absolutely accurately either."

There are three stages in memory, according to modern pyschology. The first is perception, which is what we see - also what we hear, taste, touch and smell. This in itself is a selective process. From the start we can fail to encode detail or simply not notice something, so the information going in isn't accurate. Secondly there's storage. We know we forget things over time, but we also revise our memories and re-write them to fit in with new ideas.

Finally there's the retrieval stage, where the brain searches out information. When you remember something, lots of different parts of the brain work together and from that emerges the mental representation that is going to be your experience of a memory. Every time you recall something, you reinterpret it all over again. And in every reconstruction process there are many opportunities for error.

'Empty the head'

In a crime situation memory is influenced by many factors such as stress, the presence of a weapon and even just the desire to help police solve the crime.

"Police know how fallible the memory can be," says Steve Retford, a former head of the investigative skills unit at GMP and now specialist interviewing adviser with the force.

"They also know this is usually not through mischievousness on the part of the witnesses, but through stress and shock."

Take the case of Jean Charles de Menezes, shot at Stockwell Tube station in 2005 by police who mistook him for a suicide bomber. Eyewitnesses said he had vaulted a ticket barrier when running away from the police. In fact it was later shown by CCTV that Mr Menezes had walked through the barriers, having picked up a free newspaper, and only ran when he saw his train arriving.

Memories are reconstructed subconsciously

In some cases erroneous eyewitness testimony has led to false imprisonment. In the 1970s, the overturning of several eyewitnesses cases resulted in the Devlin Committee's investigation of identification evidence. It found many witnesses overstated their ability to single out the right person.

What this latest research has proved is the extent of how fallible the memory can be, which is "massively important", say those involved.

"That the memory is vulnerable is not new," says Dr Pike. "But it is so important that we know how fallible it is and in what ways. By understanding this better we can design police techniques that make the most of memory."

For the police, the findings of the project are essential because eyewitnesses are still at the heart of most investigations - even with the growth of CCTV.

"Eyewitnesses are our lifeblood and without them you are usually stuffed," says Mr Retford. "Creating the right environment and using the correct psychological tools to get accurate evidence is vital. You have to be on top of your game and really empty the head of all the detail you need."

Below is a selection of your comments.

This article just goes to prove how careful the police need to be when piecing together eyewitness statements and really bears out the painstaking number of hours that are required for statements to be checked and re-checked in order to come to the right conclusion when any sort of serious crime has been committed.Keith Parker, Edinburgh, Scotland

This is why the death penalty is seriously flawed. Unless hard medical/forensic evidence and/or video tape can be produced, no country should be allowed to execute anyone - even if they do have "eyewitness testimony". And even then, it's debatable, but that's another story... Let's just be grateful it doesn't apply in the UK!Gemma, Crawley, UK

Being interested in psychology as well as crime/forensics I have often played that game with myself. Recalling an incident - often very recent - and trying to pin down the details. It is astonishingly hard. Observational skills are a part of many careers but often the observer is safe, comfortable and well aware of what they are trying to observe. Unexpected and dangerous situations don't do the memory any favours at all. You can see why the police like cameras in more situations than the public might appreciate. I'd recommend anyone to try it themselves. Sit in a cafe, observe an interaction between a few people then, a little later, try to descibe it. Sandy Fox, Derby, UK

I recently saw a burglary and embarassingly, I couldn't tell the police anything about the car model or registration. I wasn't even sure about the colour. I did, however, remember that the getaway driver wore a gold sovereign ring on the middle finger of his left hand. It seems like a weird thing to have focussed on, and I don't think that it helped much...!Sue, London

Hilarious - "we only started to get suspicious when the police turned up really quickly"Graham, Aberdeen UK

I witnessed a robbery and took a mental note of the car make & model, colour and the registration plate. I was amazed that someone next to me couldn't even get the colour of the car correct.Mike, Potters Bar, UK

It brings the strength to having high qulaity cctv cameras. You can't rely on people and what they claim, because people have agendas.John Evans, London

Surly this type of research should make it mandatory for CCTV to be in use in all public places and spaces. Clearly if we are sending the wrong people to jail based on eye witness accounts the law should be more measured in the relevance of such accounts. This also explains why it's so easy for barristers to discredit eye witnesses. Also this accounts for why I've been watching my football team all my life, they are clearly rubbish but when I watch them they play great!Martin, London

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